I remember reading or hearing an interview with Dennis from the mid-60s where he mentions that he doesn't drink, which I thought was kind of odd, considering what ended up happening. I assume he was taking drugs that early (as Brian was), but I wonder when the drinking started. It occurred to me that he might be lying to the reporter with the fans in mind, but then, Dennis seemed to be incapable of BS, much like Brian.
What energy he had in the 60s.
Dennis started drinking in his early teens, but there were also periods where he was totally clean. It seems he drank a lot of alcohol starting in the early '60's and also dabbled with weed and pills back then, but by '65 he was a non-drinker and vocal anti-drug type. After that he'd be on and off...he started smoking weed regularly in late '66 or '67 and got into LSD briefly in '67 - '68. After the Manson thing he stayed pretty straight when he first found Barbara, didn't even smoke much weed...but then '73 found him drinking hard and constantly...and again in '74 - '75 he found some time to be relatively clean again, and also fell off the wagon really hard a few times during those years with Quaaludes and coke. But overall in 1975 Dennis was really healthy. Starting in '76 it was pretty much party full time, the list is too long, he tried everything. But up until then he would go six months or even a year at a time trying to be healthy. I think the cigarette habit followed him from high school and throughout his life, although there were even a couple of periods where he put those down.